1. Field of the Invention
The present invention relates to a pulsed load cooling method and refrigerator.
The invention in particular relates to a pulsed load method for cooling a component of a “Tokamak”, i.e. a component of an installation for intermittently generating a plasma, the method employing a cooling device that subjects a working fluid such as helium to a working cycle comprising: compression; cooling and expansion; heat exchange with the component; and heating, the cooling power produced by the cooling device being increased to a relatively high level when the Tokamak is in a plasma generation phase whereas the cooling power produced by the cooling device is reduced to a relatively low level when the Tokamak is no longer in a plasma generation phase.
The invention more particularly relates to a pulsed load cooling method and refrigerator for cooling a component of a Tokamak, i.e. a component of an installation for intermittently generating a plasma.
2. Related Art
A Tokamak (Russian acronym for “Toroidalnaya Kamera c Magnitnymi Katushkami”) is an installation capable of producing the physical conditions necessary for obtaining fusion power. In particular, a Tokamak intermittently produces plasma, i.e. ionized gas that conducts electricity.
The cooling requirements of Tokamaks depend on their highly transitory operating state. A Tokamak produces plasma in discontinuous, repeated bursts. The plasmas are generated cyclically at regular intervals or else randomly, on request.
This operating mode requires what is called “pulse load” cooling, i.e. very substantial cooling power is required for a very short amount of time (during the plasma generation phase), this high cooling demand being followed by a longer period (until the next plasma is generated) during which there is little need for cooling.
Tokamak refrigerators are therefore designed to meet the requirements of this operating mode. Thus, these refrigerators employ what is called an “economizer” mode, producing liquid helium in the periods between plasmas. The liquid helium produced is stored in a reserve that will be consumed by boiling to cool a component of the Tokamak during plasma generation phases.
When the period between two plasmas is sufficiently long, the maximum filling level of the liquid helium reserve is reached before the following plasma. The cooling power of the refrigerator may then be reduced, thereby saving a substantial amount of power. In a conventional solution, the power of the refrigerator is minimized by reducing the pressures of the cycle (i.e. by reducing the pressure level of the compression of the helium in its working cycle). The power of the refrigerator may also be decreased or increased by changing the cycle flow rate when a frequency variator is used (i.e. the flow rate of helium through the working cycle is selectively decreased or increased).
A heater is generally provided in the liquid helium reserve. This heater is activated in order to consume excess cooling power, so as to keep the liquid level constant or at least below a maximum threshold.
Conventionally, the transition between power regimes (increase or decrease in the cooling power produced) is requested depending on the activation power of the heater, i.e. the electric control signal of the heater is interpreted using a “heating curve” that defines the pressure setpoint of the cycle and/or the frequency setpoint of the variator of the compressing station of the refrigerator.
When a new plasma is generated, the refrigerator is made to produce a maximum refrigeration power either manually (by an operator), or as a function of the “heating curve” of the heater.
When the plasma has been extinguished and the cooling power required is lower, the return of the refrigerator to a regime producing less cooling power is generally achieved automatically, when no power is being supplied to the heater.
Document WO 2009/02740512 describes a method for regulating the cryogenic power delivered to a consumer by a refrigerator, based on the cooling power produced by the refrigerator.
Although these operating modes are satisfactory overall, the power consumption of the refrigerator remains high.